Amplifier



Sept. 14, 1937. D. G. BURNSIDE 2,092,874

AMPLIFIER Filed Oct. 25, 1953 0'0 0 0'0 0 com on 4, INVENTOR Don G.BURNS|DE I BY 6 j MVW ATTORNEY Patented Sept. 14, 1937 UNHTED STATES ANI'PLIFIER lion G. Burnside, East Orange, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 2a, 1933, S ial No. 694.721

1 Claim. (01. 179-171) The present invention relates broadly to amplifiers and more particularly to a novel circuit arrangement utilized as a driver and phase changer for supplying alternating current voltage to the grids of tubes connected resistance coupled pushpull.

It is known in the art that push-pull transformers are expensive and that a system which would eliminate the use thereof while still retaining the advantages of push-pull amplification is greatly to be desired.

With the above in mind, the present invention makes use of a driver circuit for the push-pull circuit which includes a tube having within a single enclosure a cathode, two grids and two anodes. type 79, type 19 and type 53 tubes and consist of two high-mu tricdes in a single bulb. The two triode units are identical and except for a common cathode are distinct each from the other. The characteristics of these tubes are such that they may be readily adapted for use as phase inverters and it is an object of the present invention to devise a circuit arrangement by means of which the outputs of one of these tubes may be impressed upon a push-pull amplifier.

The single figure in the drawing shows a preferred embodiment of the invention.

In the drawing, a pair of tubes T1 and T2 are shown provided with a push-pull output circuit represented generally by primary I2 of an output transformer. Each tube comprises an anode, a cathode and a control grid, the space current for the tubes being furnished by a suitable source,

not shown, having terminals B and 3+. Across the source is connected a voltage divider R7, R8.

The cathodes 8 and 9 of tubes T2 and T1 have a common connection to ground through a bias resistance Rs while the anodes 6 and H of these tubes are connected to the B+ side of the source by a connection from terminal B+ to the center point of winding l2. Tube T1 is provided with a grid leak resistor R4 connected between grid Ill and the grounded side of Rs while tube T2 is provided with a similar grid leak resistor R5 which is connected between grid 1 and the grounded side of resistor R6.

The driver circuit comprises a tube T provided 50 with a cathode l, two grids 2 and t and two anodes 3 and 5. Cathode l, grid 2 and anode 3 form one unit of the tube while cathode l, grid These tubes are known in the art as terminals shown and a resistorRi. This resistor which is, in fact, a section of the Voltage divider provides the proper bias voltage. Cathode l'is grounded at G in customary fashion and a'usual signal by-pass condenser C4 is shunted across re- 5 sistor R7. The output circuit for the first unit comprises a connection between anode 3 and the B+ side of the source and includes a plate load or plate resistor R1. The anode end of resistor R1 is connected to grid In of tube T1 through 10 a coupling condenser C2 so that signals impressed on the grid 2 of tube T put amplified voltage on grid Ill. At the same time, a voltage 180 degrees vout of phase with voltage on grid 2 is applied to grid 5 of the second unit through a connection 15 from anode 3 to cathode I including a condenser C1 in series with a resistor R2 and a connection from grid 4 of the second unit to a point of resistor R2. I

The output circuit of the second unit comprises 20 a connection from anode 5 to the B+ side of the source and includes a plate resistor or load R3. The anode side of resistor R3 is connected to grid l of tube T2 by means of a coupling condenser C3. Resistor R2 is arranged so as to act as a 25 grid leak for the second unit. Audio voltage of proper amplitude for grid 4 is derived by means of a variable tap on the resistor R2 as shown.

With the arrangement shown, the voltage developed across the plate load R1 is 180 degrees 30 out of phase with the voltage developed across plate load R3, hence, the grids Ill and 1 of the two output tubes T1 and T2 can, therefore, be resistance coupled to the two resistors R1 and R3.

If the two tubes T1 and T2 are identical then 35 the tap on resistor R2 is adjusted to equalize the voltages on resistors R1 and R3 since under these circumstances the voltages impressed upon grids It and i must be of opposite phase and equal amplitude for the push-pull amplifier to operate 40 properly.

It is obvious now that if the two tubes T1 and T2 are not identical the tapon resistor R2 may be adjusted so that equal outputs from tubes T1 and T2 are obtained.

It is, of course, obvious to any one skilled in the art that tubes T1 and T2 may be replaced by a single tube like tube T and that tube T may be replaced by two separate tubes.

While only one embodiment has been shown l for purposes of illustration, to those skilled in the art many variations of the system and details of the apparatus herein described are at once obvious and the fact that specific arrangements have been illustrated is not to be taken as indicating any intention of limiting the invention thereto.

I claim:

In an amplifier, a pair of electronic tubes provided with anode, cathode and control grid electrodes, a push-pull output circuit therefor, a pair of resistance elements in series connecting the control grids of both tubes, a common cathode lead and a connection between the common cathode lead and a point intermediate the resistance elements, including a. common grid bias resistor, a driving circuit comprising an electronic tube provided with at least a cathode, two control grids and two anodes, disposed with relation to each other so that the cathode, one grid and one anode thereof form a first amplifying unit while the cathode, the other grid and the other anode form a second amplifying unit, a single source of space current for all of said tubes, said source being provided with positive and negative terminals, connections between the anodes of said pair of electronic tubes and the positive terminal of the source, an input circuit for the first unit including means for connecting a source of energy to be amplified, an output circuit for the first unit comprising a connection between the anode thereof and the positive terminal of the source, including a plate resistor element, means comprising a coupling condenser for connecting a point of the last named circuit connection to the control grid of one of said pair of electronic tubes, a connection between the anode of the first unit and the negative terminal of the source of space current, including a condenser and a resistor in series, means comprising a variable tap device for connecting the grid of the second unit to any desired point of said resistor whereby signal energy is impressed upon the grid of the second unit in phase opposition to the signal energy impressed upon the grid of the first unit, an output circuit for the second unit comprising a connection between the anode thereof and the positive terminal of the source, said last-named output circuit including a load resistance means comprising a coupling condenser for connecting a point of the last-named output circuit to the grid of the other of said pair of electronic tubes, and a bias impedance device connected between the negative terminal of the source and the cathode of the driver circuit electronic tube, said bias impedance being included in both the input and output circuits of the two amplifying units whereby the same bias potential is impressed upon the control grids of the two amplifying units.

DON G. BURNSIDE. 

